Most will recall the rumblings of Mount St. Helens earlier this year. Since then, an unusually smooth and swiftly growing lava dome within the crater is being considered by scientists to be an "extraordinary and perplexing" event with an unknown outcome. While no major eruptions are expected in the near term, the dome's construction can be likened to a "runaway freight train in terms of the steady forces involved." "There's a truckload of hot rock coming out of the mountain every second," said Dan Dzurisin of the U.S. Geological Survey (USGS). "We're scratching our heads about it."

The September activity caused the original dome inside the crater to grow a welt on its south side. That welt has quickly become a separate dome, and looks different, part of it being as smooth as an "overturned ship." The size of this new dome is now bigger than an aircraft carrier, with a central head between and above two shoulders. Inside a crust of about 10m (33ft.) thick, the dome is loaded with magma, scorching molten rock. The whole structure is pushing its way south as it grows, "bulldozing its way into the glacier," Mr. Dzurisin said, "shoving it out of the way, cracking it, lifting it."

Scientists simply do not know what the mountain has in store. An eruption like the one in 1980 is not expected, but if this new dome continues to rise, an eventual collapse, causing magma and ice to mix and releasing a large ash cloud up to 40,000 feet (12 kilometers), would be significant. "Collapses," said USGS researcher Cynthia Gardner, "can happen without warning."